SAPPORA, Japan - More than 42 people suffered injuries in a massive explosion at a bar in the northern Japanese city of Sapporo on Sunday.

The large explosion, which led to a number of buildings in the area to collapse, occurred at 8.30 pm local time on Sunday (11.30 am GMT) in Sapporo, which is the capital city of Japan's main northern island of Hokkaido.

Authorities quoted in Japan's Kyodo news agency said that the blast ripped through a two-storey building that featured the Izakaya bar in the Toyohira district of Sapporo.

The explosion, which caused widespread alarm in the city, especially in the vicinity of the bar - left 42 people injured, with one of them being in a critical condition.

Police in Sapporo told reporters that a huge emergency operation had been initiated following the explosion.

Photos from the site of the explosion, that emerged on the social media, showed the area covered in dark smoke, as debris from collapsed buildings and shattered windows were scattered around.

According to officials, over 20 fire engines had been deployed to the area post the blast, with firefighters battling the flames and tackling the collapsing buildings.

Further, the police teams that rushed to the site of the explosion, sealed off the entire area, which has a mix of residential buildings and dining establishments.

Officials said the area, which is about 3 kms south-east of the city centre, had been cordoned off over the possibility of more explosions.

While the police have not revealed the cause of the explosion so far, some local reports suggested a possible gas blast.

A report in The Japan Times quoted some witnesses in the area as saying that the explosion sounded like thunder and caused structures of rattle, damaging buildings and cracking windows.

Other witnesses describing the scene said that they smelled gas after the explosion struck the building.

However, the police in Japan have refused to reveal any further details and said that the cause of the explosion was being investigated.